add dependency on story_title.tw2

Rakefile

@@ -73,7 +73,7 @@ file 'story_title.tw2' do
 end
 
 desc 'export sub files to Twine 2'
-task export: %w(bundle_install storyjs story.tw2) do
+task export: %w(bundle_install storyjs story.tw2 story_title.tw2) do
   files.each do |file|
     IO.write file.wrapper_file, <<~EOF
       ::StoryTitle